\ FUNDAMENTAL PEINOIPLES. 41 



cutaneous sensibility, and if the current be sufficiently strong. 

 The same phenomena are repeated at the moment of separating 

 tlie rheophores from the skin. In order to avoid this electro- 

 cutaneous excitation during the faradization of muscle, it is neces- 

 sary to avoid establishing the current until the contact between 

 the skin and the rheophores is complete. (I shall hereafter point 

 out the precautions to be taken in order not to produce cutaneous 

 sensations.) 



(&). The moist rheophores act invariably upon the cutaneous 

 nerves when placed over their course. In order to study the 

 phenomena resulting from their excitation, the tension of the 

 current should not be sufficient to penetrate to the muscles. 

 The faradization of a cutaneous nerve produces a sensation which 

 is continued along the course of the nerve, beyond the point 

 excited, to the finest ramifications ; where it occasions tingling 

 and pricking, proportionate to the degree of intensity of the 

 current, and the rapidity of the intermittences. The sensations 

 are also more acute when the nerves are excited at a point near 

 to their finest ramifications : thus they are produced more strongly 

 by faradization of the collateral nerves of the fingers and toes, 

 than of the cutaneous nerve higher up. The excitability of the 

 cutaneous nerves differs greatly. It is carried to the highest 

 degree in some of them; the frontal, for example, derived from 

 the opthalmic of Willis, cannot be touched without provoking 

 acute pain in the faradized point, spreading from thence to all 

 the ramifications. In other nerves faradization is only appreciable 

 by the extension of slight tingling over the regions of their distri- 

 bution. The cutaneous nerves of the limbs are generally in this 

 latter condition. 



A knowledge of these phenomena renders it possible to dis- 

 tinguish the complex sensation, due to the simultaneous excita- 

 tions of cutaneous nerve and muscle, from that which is the result 

 of the excitation of muscle alone. Indeed, when the moist rheo- 

 phores are placed on the plane of a muscle, and over an excitable 

 cutaneous nerve, the participation of the latter is shown by the 

 tingling or pricking which extends along its ramifications, and by 

 a special pain, if the nerve be very sensitive, limited to the point 

 excited. When the rheophores are so moved as to avoid the 

 cutaneous nerve, the tinglings and the local pain cease instantly, 

 and allow the purely muscular sensations to be perceived. 



§ II. Is it possible to concentrate the electric force in a muscle f 



We are met here by an objection seemingly very serious, which 

 would present itself naturally to all minds, and which nearly 



